Thermionic emitter for high frequency tube apparatus



March 17, 1964 J. K. MANN 3,125,701

THERMIONIC EMITTER FOR HIGH FREQUENCY TUBE APPARATUS Original Filed July 17, 1958 iii'HHl FIG INVENTOR JSEPH K-MANN BY A TORNEY United States Patent 3,125,701 THERMIONIC EMHITER FOR HTGH FREQUENCY TUBE APPARATUS Mann, Palo Alto, Calif., assignor to Va-rian Palo Alto, Calif., a corporation of Original application .lnly 17, 1958 Ser. No. 749,225, now Patent No. 2,994,009, dated July 25, 1961. Divided and this application May 4, 1960, Ser. No. 26,370

7 Claims. (Cl. 315-) The present invention relates in general to high frequency tube apparatus and more specifically, to a novel high frequency, high power velocity modulation tube which is extremely useful for providing a continuous wave output at high average powers and which is easily tunable over a wide frequency range. Such tubes are especially useful as output tubes in tropospheric forward scatter communication links, and for transmitting tubes covering the UHF-TV band. This application is a divisional of my copending application, Serial No. 749,225, filed July 17, 1958, for Improvements in High Frequency Tube Apparatus, now U.S. Patent No. 2,994,009, issued July 25, 1961.

The present invention provides a high power multicavity klystron amplifier capable of delivering average output powers in the order of 12 or more kw. and at the same time have the greatly enhanced tuning range of approximately 40 percent.

The principal object of the present invention is to provide a novel high power high gain amplifier tube apparatus having exceptionally wide frequency tuning range which is especially useful, for example, in UHF-TV broadcasting and forward scatter communication.

One feature of the present invention is the provision of a novel radiant cathode heater assembly wherein an uncoated heating element is held against the surface of a dielectric member which is positioned in close proximity to the backside of a cathode emitter whereby uniform support of the heating element is greatly facilitated thereby enhancing its longevity and reliability.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein,

FIG. 1 is a longitudinal cross sectional view of a portion of a tube structure employing features of the present invention,

PEG. 2 is an enlarged detailed View of a portion of the structure of FIG. 1 delineated by line 22,

FIG. 3 is a cross sectional view of a portion of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows, and

FIG. 4 is an enlarged detail of that portion of FIG. 2 delineated by line 4.

Referring now to the drawings there is shown in FIG. 1 a novel tube apparatus of the present invention. More specifically, a segmented tubular cathode assembly 1 provides a source of electrons which are formed into a pencil-like beam and projected longitudinally of the tube apparatus. A plurality of rectangular cavity resonators including an input resonator 2, second and third buncher cavities 3 and 4, and an output cavity, not shown, are centrally apertured to allow the passage of the pencillike beam of electrons therethrough.

The individual cavity resonators are tunable over a wide range via a plurality of novel tuner assemblies which form the subject matter of the aforementioned parent patent. The beam after passing through the output cavity resonator is collected in a collector assembly, not shown. The thermal energy generated by the impinging electrons Joseph K.

Associates, California "ice within the collector is carried away by a fluid coolant circulated through the collector assembly 7.

RF. signal energy, which it is desired to amplify, is fed to the input cavity 2 via a vacuum sealed coaxial connector -8. The signal energy velocity modulates the beam as it passed through the input cavity 2. The velocity modulation of the beam is transformed into current density modulation in the drift spaces between the input cavity 2 and the first buncher cavity 3. Buncher resonators 3 and 4 further velocity modulate the beam to produce greater current density modulation of the beam at the output cavity. The output cavity extracts R.F. energy from the current density modulated beam.

The output RF. energy is coupled outwardly of the output resonator via a vacuum sealed RF. coaxial line, not shown, and fed to a suitable load, not shown, such as, for example, an antenna. The load is coupled to the coaxial line via a coaxial connector assembly, not shown. A magnetic solenoid, not shown, circumscribes the central part of the tube apparatus, containing the cavity resonators, for providing a strong axial magnetic field longitudinally of the tube for confining the pencil-like beam of electrons.

The cathode assembly 1 (FIGS. 24) includes therewithin a concave tungsten impregnated barium aluminate cathode emitter button 101 operating at approximately 1000l C. and carried from its peripheral edge via a refractive metal ring 102 as of tungsten riding within a peripheral recess in the cathode emitter 101 and being spot-Welded to a hollow cylindrical button support 103 as of tantalum. A cathode heating element 104 as of, for example, bore 0.030" diameter tungsten wire is wound in a double physical configuration. The heating element 104 operates at 1700 C. and is held tightly against a refractory dielectric disk or base plate member 105 as of alumina ceramic via a refractory dielectric rod 106 as of, for example, sapphire extending across the double spiral wound heater 104. The rod 106 is held tightly against the heating element 104 by a flat ground on the backside of the cathode emitter 101.

The ceramic disk 105 affords a uniform electrically insulated support for the bare heater element 104 without conducting excessive heat from the element 104. The sapphire rod 106 assures uniform support for the heating element 104 without shorting the element 104 and without intercepting excessive radiant heat therefrom. The interturn spacing of the heater filament 104 allows for creepage of the filament 104 without shorting adjacent turns.

A transverse cathode header 107 as of tantalum has affixed thereto the hollow cylindrical cathode button support 103 and is secured at its peripheral edge to a hollow cylindrical focus electrode 108 as of, for example, titanium. The transverse cathode header 107 and dielectric disk 105 as of alumina are suitably apertured to allow the cathode heater leads 104 to extend through the cathode header 107.

One heater lead 104 is spot-welded to a metal tab 109 secured to the backside of the cathode header 107. The other heater lead 104 is secured via a crossover conducting bar 111 to a center heater lead 112. The center heater lead 112 is carried at its flared end from the centrally apertured ceramic disk 105. The flared end of the center conductor 112 is pulled tightly against an inner shoulder of the apertured ceramic disk 105 via an annular ceramic spacer 113 positioned between the transverse header 107 and the transversely extending conducting bar 111.

The cylindrical focus electrode 108 is carried at the end of a hollow cylindrical cathode support 114 which is closed off at the other end thereof via a heater cup 115 centrally apertured to carry therefrom an exhaust tubula- 3 tion 116 which is suitably pinched off after the tube has been evacuated. The heater cup 115 is electrically insulated from the tubular cathode support 114 via an annular insulator 117 as of, for example, ceramic.

A cup-shaped heater terminal 118 as of, for example, aluminum is provided with threads internally thereof substantially at the open end thereof for mating With the external threads of a heater terminal adaptor 119 carried from and externally of the heater cup 115. The center heater lead 112 is provided with two supporting leg portions 121 and 122 which are fixedly secured as by, for example, spot-welding to the heater cup 115 and which are jointed together as by, for example, spot-welding at the other ends thereof to form a lower portion of the center heater lead 112. The lower portion of the heater lead 112 is joined to the upper portion via a metal strap 123 spot-welded to the two heater lead portions.

The cup-shaped heater terminal 118 makes contact with one terminal of the heater current source, not shown, and the other terminal of the heater source, not shown, makes contact with a centrally apertured cup-shaped cathode terminal 124 carried from the cathode support 114 via an annular cathode adaptor ring 125 and a plurality of machine screws 126. The heater current thus flows into the heater terminal 118 thence via heater cup 115 and the two legs 121 and 122 of the heater lead 112 and heater crossover bar 111 to the spiral Wound heater element 104. The current returns from the heater element 104 via tab 1&9 and the cylindrical cathode support 114 thence via the annular cathode adaptor ring 125 and machine screws 126 to the cup-shaped cathode terminal 124.

A high voltage hollow cylindrical cathode insulator as of, for example, ceramic is carried at one end thereof via a first annular frame member 128 as of Kovar Which is fixedly secured in a vacuum tight manner at one end thereof to the outer peripheral edge of the cathode adaptor ring 125 as by, for example, a heliarc weld. The other end of the high voltage insulator 127 is secured to a second annular insulator frame member 129 as of, for example, Kovar. The window frame member 129 is in turn sealed to a hollow cylindrical magnetic cathode shield 131 as by, for example, brazing. The cathode magnetic shield is made of a magnetically permeable material as of, for example, iron and serves to shield the emitter button 101 from the beam confining magnetic field. The cathode shield 131 is sealed to a cylindrical cathode shield adaptor 132 via the intermediary of a heliarc welded flange seal 133. The cylindrical cathode shield adaptor 132 is carried from the annular magnetic pole piece 43 as by, for example, brazing.

A centrally apertured cup-shaped cathode seal protector 134 circumscribes the heliarc welded cathode flange seal 133 and is carried from the annular pole piece 43 via a plurality of screws 135 spaced about the seal protector 134. A transverse wall 136 of the input cavity resonator 2 serves as a portion of the centrally apertured anode of the tube apparatus and is sealed to and carried from the annular pole piece 43 via a heliarc welded flange seal 137.

In operation a potential of approximately 16 kv. more negative than the potential of the anode 136 is applied to the cathode button 191 via cathode terminal 124. A beam of electrons is caused to be emitted from the cathode emitter 101 and projected through the anode 136 and into the flared entrance of the first drift tube section 17. At this point the beam enters the beam confining magnetic field which is directed longitudinally of the tube and serves to confine the beam against its radially exerted space charge expansion forces.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A thermionic particle emitter apparatus including, a thermionic particle emitter for supplying charged particles, a filamentary uncoated heater element for radiantly heating said particle emitter without operating said element at an excessively high temperature, a first refractory insulating member, a second refractory insulating member, said uncoated filamentary heater element held inbetween said first refractory insulating member and said second refractory member, and said heater element disposed at the backside of said particle emitter to provide a rigid heater support which minimizes the possibility of heater shorting and allows a maximum of projected heater area on the backside of said particle emitter thereby reducing the operating temperature of the heating assembly.

2. The apparatus according to claim 1 wherein said second refractory member is disposed inbetween said heater element and said particle emitter and said second refractory insulating member portion having a normal projected area on the backside of said particle emitter which is substantially less than the projected area of said first refractory insulating member on said particle emitter.

3. The apparatus according to claim 2 wherein said first refractory insulating member is formed in the shape of a circular plate, and said second refractory member is a dielectric refractory rod clamping said uncoated heater element inbetween said rod and said circular plate.

4. The apparatus according to claim 3 wherein said circular plate is made of alumina ceramic and said refractory rod is made of sapphire.

5. In a cathode structure, a thermionic particle emitter member for supplying charged particles, a filamentary uncoated heater element for radiantly heating said particle emitter, a refractory insulating base plate, a refractory rod, said uncoated filamentary heater element being held inbetween said base plate and said refractory rod, said refractory rod serving to clamp said filamentary heater element against said base plate, and said heater element disposed at the back side of said particle emitter to provide radiant heat for said particle emitter, said rod being disposed inbetween said particle emitter and said heater element for holding said heater element apart at spaced locations to prevent shorting of said heater element while minimizing loss of heat from said heating element through said refractory rod member.

6. A high frequency tube apparatus including; means for forming and projecting a beam of electrons over an elongated beam path; a collecting structure disposed at the terminal end of the beam path for collecting electrons of the beam; means disposed along said beam path intermediate said beam forming means and said beam collecting means in wave energy exchanging relationship with the beam; an output terminal for extracting wave energy from said wave energy exchanging means; said beam forming means including, a thermionic particle emitter for supplying electrons, a filamentary uncoated heater element for radiantly heating said particle emitter, a refrac tory insulating base plate member, a refractory rod, said uncoated filamentary heater element being held to said base plate via the intermediary of said refractory rod, and said heater element disposed at the back side of said particle emitter remote from the beam side of said particle emitter to provide radiant heat for said particle emitter, and said refractory rod being disposed inbetween said particle emitter and said heater element for holding said heater element apart at spaced locations to prevent shorting of said heater element while minimizing loss of heat from said heating element through said refractory rod.

7. The apparatus according to claim 6 wherein said emitter member comprises a concave circular segment,

said uncoated heater element is spirally wound about an axis coaxial with the axis of revolution of said circular emitter segment, said refractory rod member is radially directed across said spirally Wound heater element, and wherein said refractory rod has a normal projected area on the back side of said concave particle emitter segment which is a small fraction of the projected area of said base plate on said particle emitter.

References Cited in the file of this patent UNITED STATES PATENTS Kapteyn Oct. 5, 1937 Clavier et a1. Dec. 31, 1940 Segerstrorn Ian. 1, 1946 Pearce et al July 6, 1948 Koch June 6, 1950 Ward Dec. 16, 1958 

6. A HIGH FREQUENCY TUBE APPARATUS INCLUDING; MEANS FOR FORMING AND PROJECTING A BEAM OF ELECTRONS OVER AN ELONGATED BEAM PATH; A COLLECTING STRUCTURE DISPOSED AT THE TERMINAL END OF THE BEAM PATH FOR COLLECTING ELECTRONS OF THE BEAM; MEANS DISPOSED ALONG SAID BEAM PATH INTERMEDIATE SAID BEAM FORMING MEANS AND SAID BEAM COLLECTING MEANS IN WAVE ENERGY EXCHANGING RELATIONSHIP WITH THE BEAM; AN OUTPUT TERMINAL FOR EXTRACTING WAVE ENERGY FROM SAID WAVE ENERGY EXCHANGING MEANS; SAID BEAM FORMING MEANS INCLUDING, A THERMIONIC PARTICLE EMITTER FOR SUPPLYING ELECTRONS, A FILAMENTARY UNCOATED HEATER ELEMENT FOR RADIANTLY HEATING SAID PARTICLE EMITTER, A REFRACTORY INSULATING BASE PLATE MEMBER, A REFRACTORY ROD, SAID UNCOATED FILAMENTARY HEATER ELEMENT BEING HELD TO SAID BASE PLATE VIA THE INTERMEDIARY OF SAID REFRACTORY ROD, AND SAID HEATER ELEMENT DISPOSED AT THE BACK SIDE OF SAID PARTICLE EMITTER REMOTE FROM THE BEAM SIDE OF SAID PARTICLE EMITTER TO PROVIDE RADIANT HEAT FOR SAID PARTICLE EMITTER, AND SAID REFRACTORY ROD BEING DISPOSED INBETWEEN SAID PARTICLE EMITTER AND SAID HEATER ELEMENT FOR HOLDING SAID HEATER ELEMENT APART AT SPACED LOCATIONS TO PREVENT SHORTING OF SAID HEATER ELEMENT WHILE MINIMIZING LOSS OF HEAT FROM SAID HEATING ELEMENT THROUGH SAID REFRACTORY ROD. 